Geoscience Reference
In-Depth Information
Temperature (°C)
Figure 15.17
Ground temperature regime in
permafrost.
Source: After Brown (1973)
0
-5
-4
-3
-2
-1
0
1
2
3
Active layer
5
Mean annual
ground temperature
Permafrost
table
Maximum
temperature
Minimum temperature
10
Level of zero
annual amplitude
15
Permafrost
20
Geothermal gradient
25
Permafrost base
30
35
depths of 10-15 m, at the
level of zero annual amplitude
.
Below this level, temperatures increase according to the
geothermal gradient
.
The
active layer
is the upper part of the ground that
freezes and thaws each year, i.e. where the maximum
temperature is above 0
C. Its thickness varies from several
metres in bedrock with a high thermal conductivity to less
than 25 cm in vegetated peaty terrain, where insulation
supplied by the organic layer restricts the flow of summer
heat into the ground (
Plate 15.16
).
Climate is the main
factor determining the distribution, temperature and
thickness of permafrost. The spatial patterns of mean
annual ground temperature and mean annual air
temperature are similar, but the ground temperature is
generally 2
C higher, and shows larger local
variations. The relationship between ground temperature
and climate is governed by the surface energy balance,
which in turn depends on site-specific conditions such as
slope, aspect, vegetation, snow cover, surface materials, the
C to 4
Arctic archipelago. The brown 'active layer' is very wet in
summer, and the blue ice lenses of the permafrost are
separated by frozen brown soil.
Photo: Ken Atkinson
